Method And System For Time Interleaved Analog-To-Digital Converter Timing Mismatch Estimation And Compensation

ABSTRACT

Methods and systems for time interleaved analog-to-digital converter timing mismatch calibration and compensation may include receiving an analog signal on a chip, converting the analog signal to a digital signal utilizing a time interleaved analog-to-digital-converter (ADC), and reducing a blocker signal that is generated by timing offsets in the time interleaved ADC by estimating complex coupling coefficients between a desired digital output signal and the blocker signal utilizing a decorrelation algorithm on frequencies within a desired frequency bandwidth. The decorrelation algorithm may comprise a symmetric adaptive decorrelation algorithm. The received analog signal may be generated by a calibration tone generator on the chip. An aliased signal may be summed with an output signal from a multiplier. The complex coupling coefficients may be determined utilizing the decorrelation algorithm on the summed signals. A multiplier may be configured to cancel the blocker signal utilizing the determined complex coupling coefficients.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of application Ser. No. 14/920,699filed on Oct. 22, 2015, which is a continuation of application Ser. No.14/590,250 filed on Jan. 6, 2015, now U.S. Pat. No. 9,172,386, which isa continuation of application Ser. No. 13/936,385 filed on Jul. 8, 2013,now U.S. Pat. No. 8,928,507, which makes reference to and claimspriority to Provisional Application No. 61/668,813 filed on Jul. 6, 2012Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for time interleaved analog-to-digital convertertiming mismatch estimation and compensation.

BACKGROUND OF THE INVENTION

Satellite television has advanced from an expensive hobbyist-onlytechnology to a ubiquitous residential television service that rivalscable television, primarily due to reductions in the cost of satellitetelevision reception technology.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for time interleaved analog-to-digital convertertiming mismatch estimation and compensation substantially as shown inand/or described in connection with at least one of the figures, as setforth more completely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary communication device with analog todigital converter timing offset estimation and compensation, inaccordance with an embodiment of the invention.

FIG. 2 is a diagram illustrating an exemplary analog to digitalconverter with two paths, in accordance with an embodiment of theinvention.

FIG. 3 is a diagram illustrating alias signals from blockers resultingfrom timing offsets in a time interleaved analog to digital converter,in accordance with an embodiment of the invention.

FIG. 4 is a diagram illustrating exemplary ADC timing offset estimationand compensation circuitry, in accordance with an embodiment of theinvention.

FIG. 5 is a diagram illustrating exemplary ADC timing offsetcompensation-only circuitry in time-domain, in accordance with anembodiment of the invention.

FIG. 6 is a diagram illustrating exemplary ADC timing offsetcompensation-only circuitry in frequency-domain, in accordance with anembodiment of the invention.

FIG. 7 is a flow diagram illustrating exemplary steps in an aliasingcompensation process, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system fortime interleaved analog-to-digital converter timing mismatch estimationand compensation. Exemplary aspects of the invention may comprisereceiving an analog signal on a chip, converting the analog signal to adigital signal utilizing a time interleaved analog-to-digital-converter(ADC), and reducing a blocker signal that is generated by timing offsetsin the time interleaved ADC by estimating complex coupling coefficientsbetween a desired digital signal and the blocker signal utilizing adecorrelation algorithm on frequencies within a desired frequencybandwidth. The decorrelation algorithm may comprise a symmetric adaptivedecorrelation algorithm. An amplitude of the blocker signal may beapproximated as linear within the desired frequency bandwidth. Thereceived analog signal may be generated by a calibration tone generatoron the chip for a foreground estimation and compensation. A signal maybe received from external to the chip for a background estimation andcompensation. An aliased signal may be summed with an output signal froma multiplier. The complex coupling coefficients may be determinedutilizing the decorrelation algorithm on the summed signals. Themultiplier may be configured utilizing the determined complex couplingcoefficients. The blocker signal in the time interleaved ADC may becanceled utilizing the configured multiplier. The time interleaved ADCmay comprise two ADC paths with clock signals 180 degree phasedifference. The timing offsets may comprise a deviation in the 180 phasedifference. The timing offset may be estimated based on a ratio ofamplitudes of a desired analog signal associated with the desireddigital signal and an analog signal associated with the blocker signal.A timing mismatch for a plurality of frequency channels may be estimatedutilizing the timing offset estimation and compensation circuitry.

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. As utilized herein, the terms “block”and “module” refer to functions than can be implemented in hardware,software, firmware, or any combination of one or more thereof. Asutilized herein, the term “exemplary” means serving as a non-limitingexample, instance, or illustration. As utilized herein, the term “e.g.,”introduces a list of one or more non-limiting examples, instances, orillustrations.

FIG. 1 is a diagram of an exemplary communication device with timeinterleaved analog to digital converter timing offset estimation andcompensation, in accordance with an embodiment of the invention.Referring to FIG. 1, there is shown a receiver 101 comprising a radiofrequency (RF) module 105, an analog to digital converter (ADC) 107, adigital front end (DFE) 113, and a memory 115.

The receiver 101 may be in a transceiver, for example, and may beutilized for receiving satellite television signals, cable televisionsignals, or any RF signal carrying multiple channels of data desired bya user. In an example scenario, the receiver 101 may comprise a set-topbox. In this example, the receiver 101 may be operable to receivesatellite, cable, or terrestrial television signals, down-convert andprocess the signals for communication to a display device, such as atelevision, for example.

The RF module 105 may comprise one or more RF receive (Rx) and transmit(Tx) paths for receiving signals from a satellite system, cable TVhead-end, and/or terrestrial TV antennas, for example. The RF module 105may comprise impedance matching elements, low-noise amplifiers (LNAs),power amplifiers, variable gain amplifiers, and filters, for example.The RF module 105 may thus be operable to receive, amplify, and filterRF signals before communicating them to the RF-to-baseband module 107.

The ADC 107 may comprise a wideband ADC and may be operable to convertreceived analog signals to digital signals. In an exemplary scenario,the ADC 107 may comprise a direct-sampled ADC and may comprise twoparallel ADC paths, each sampling 180 degrees out of phase with eachother, resulting in a total sampling rate that is double that of eachindividual path. For example, if each ADC path samples at 2.5 GHz, theresulting sampling rate for the signal communicated to the digital frontend 113 is 5.0 GHz.

The timing calibration module 109 may comprise circuitry operable tode-correlate signals from the parallel ADC paths in the ADC 107. In anexample scenario, the timing calibration module 109 may be integratedinto the digital front end 113. In another example scenario, the timingcalibration module 109 may be integrated in the processor 117. Slighttiming mismatches in the clock signals for the ADC paths may result inimage blocker signals when down-converted to baseband, for example. Thetiming calibration module 109 may determine a coefficient that isproportional to the timing offset between the two ADC path timingsignals. This coefficient may then be utilized by the digital front end113 to de-correlate the two desired signals from the undesired blockersignals. This process may be performed entirely in the digital circuitrywithout requiring complex analog circuitry or timing circuitry for theADC paths.

The digital front end 113 may comprise circuitry for receiving thedoublet samples from the ADC 107 and communicating them in a single datastream to the processor 117. The processor 117 may comprise a generalpurpose processor, such as a reduced instruction set computing (RISC)processor, for example, that may be operable to control the functions ofthe receiver 101. For example, the processor 117 may configure thetiming calibration module 109 to determine offsets in timing signals forADC paths. Additionally, the processor 117 may demodulate basebandsignals received from the digital front end 113.

The memory 115 may comprise a programmable memory module that may beoperable to store software and data, for example, for the operation ofthe receiver 101. Furthermore, the memory 115 may store the timingoffset coefficients determined by the timing calibration module 109.

Receivers introduce undesirable impairments to a signal when the signalis being amplified, filtered or downconverted. For example, directconversion receivers, which may also be referred to as “DCR”, “zero IFreceivers”, or “ZIF receivers”, are a very efficient way of implementinga radio receiver. However, they introduce a variety of impairments to asignal which can degrade overall performance of the system.

In an example scenario, in a time interleaved ADC, undesired imageblocker signals may be generated when the ADC clock signals do not have180 degrees phase difference. These undesired signals may be calibratedand compensated for in the receiver 101 utilizing decorrelationalgorithms, such as symmetric adaptive decorrelation (SAD) algorithms,on received signals. Three favorable conditions for this reduction ofnoise signals are (1) full spectrum capture architecture, i.e. if it isdesired to use the signals to cancel each other, both signals must becaptured; (2) the two signals are on the same chip so that a largeamount of information does not have to be passed between chips, which isthe case in a time interleaved ADC on a chip; and (3) the ability to runthe decorrelation algorithm (symmetric adaptive decorrelation and blindsource separation, for example).

Furthermore, the same process may be used for estimation in foregroundmode using a calibration tone, and background mode using an actual RFinput signal. Implementation variants include using one or more modes(foreground and/or background) and not necessarily both. For example, acalibration tone may be used to measure the nominal timing mismatch inforeground mode, and an input signal may be used in background mode totrack any drift due to temperature, voltage, or other factors affectingthe ADC timing mismatch.

The compensation method may comprise a narrowband or wideband correctionlogic using multi-tap filters in time domain or equivalently infrequency domain (e.g., using Fourier transform techniques), to applyfrequency-dependent correction once the timing mismatch is known.

In the case of multiple channel operation, for example, in a fullspectrum capture system, a shared hardware circuit that can be employedin round-robin fashion on different channels may be used to estimate theoptimal correction values, since the coupling from blockers is afunction of frequency.

The decorrelation may operate on narrow band slices of the entirefrequency band or may operate on the entire wide band frequency range.The gain and phase coefficients may then be determined for each signalto subtract the undesired signal in the digital domain.

FIG. 2 is a diagram illustrating an exemplary time interleaved analog todigital converter with two paths, in accordance with an embodiment ofthe invention. Referring to FIG. 2, there is shown a time interleavedADC 200 on a chip 210 comprising a shared buffer stage 203 and separatepaths, ADC path 1 and ADC path 2, for sampling a received analog signal.Each of the ADC paths 1 and 2 may comprise a gain stage 207A/207B and anADC 209A/209B with an input clock signal, clock (0) and clock (180). Inan example scenario, the input clock (0) signal may be at 2.5 GHz and180 degrees out of phase with the clock (180) signal, resulting in a 5.0GHz sampling rate at the digital front end (DFE) 211. Furthermore, thegain stages 207A/207B may be variable gain or a fixed gain.

There is also shown a calibration tone generator 201 for applying acalibration tone to the time interleaved ADC 200. The calibration tonemay be utilized to determine the offset in the timing signalscommunicated to the ADCs in each ADC path 1 and 2. Timing offsets may beprocess-dependent and may be essentially static, such that a calibrationmade using a calibration tone may then be applied to signals receivedduring normal operation of the receiving device. However, thermalchanges in the chip 210 may affect the timing offset, so the aliasingcompensation may also operate dynamically and thus operate on normalreceived signals during operation. The switch 205 may comprise a CMOSswitch, for example, and may be operable to switch between the RF/IFinput and the calibration tone generator 201 for background andforeground calibration, respectively.

The shared buffer 203 may comprise a gain stage for the ADC paths, whichmay communicate buffered signals to each of the gain modules 207A and207B in the ADC paths 1 and 2. The gain modules 207A and 207B maycomprise amplifiers for amplifying the buffered signals. The gainmodules 207A and 207B may comprise configurable gain levels that may becontrolled by a processor, or may comprise fixed gain levels, forexample.

The ADCs 209A and 209B may comprise circuitry that is operable toconvert analog input signals to digital output signals by makingdiscrete samples of an analog signal resulting in a digitalrepresentation of the analog signal. The frequency of the sampling maybe configured by the frequency of the clock input to the ADCs 209A and209B, and in an example scenario may be at least twice the frequency ofthe analog signal to be converted. Accordingly, the ADCs 209A and 209Bmay receive analog signals from the gain stages and may generate digitalsignals to be communicated to the digital front end 211 before beingcommunicated to the timing offset estimation module 213.

In instances where the clock (0) signal and clock (180) signal are notexactly 180 degrees out of phase, images of blocker signals at aliasfrequencies may interfere with the desired signal output. Furthermore,it should be noted that the invention is not necessarily limited to twoADC paths and may comprise any number of paths depending on the timingoffsets between paths and the decorrelation processing capabilities, forexample.

The timing offset estimation module 213 may comprise suitable circuitry,logic, and/or code that may be operable to determine complex couplingcoefficients between desired and undesired signals that may be aliasedto the same frequency range due to timing mismatch in the timeinterleaved ADC 200. The timing offset between time interleaved ADCclocks may be estimated, which may be utilized to determine correctionfactors for filters, or multipliers, to cancel aliased signals. Themultipliers, e.g., single or multi-tap filters, may be utilized tocancel the aliased signals.

The digital front end 211 may comprise circuitry that is operable toreceive the doublet samples from the ADC paths 1 and 2 and combine themto a single data stream to be communicated to a processer, such as theprocessor 117. Accordingly, the digital front end 211 may switch betweenADC outputs at a sampling frequency, F. The output signal may thencomprise a digitized signal at twice the sampling frequency of the ADCs209A and 209B, the digitized signal being communicated to the timingoffset estimation module 213 before being communicated to a processorthat may process received digital signals to demodulate, and/or performother processing techniques to the data. Furthermore, the processor mayperform timing calibration and compensation for offsets in the timingsignals clock (0) and clock (180) of the ADCs 209A and 209B.

In an exemplary scenario, the timing offset calibration and compensationprocess may be performed with a calibration signal from the calibrationtone generator 201 or may be dynamically configured during normaloperation. The frequency of the calibration signal may result in blockersignals falling within the bandwidth of the receiver. Furthermore, thecalibration and compensation may be performed entirely in the digitaldomain, thereby inducing no overhead in the RF/analog domain.

To calibrate and compensate for timing offset, the process mayapproximate the frequency dependency of the amplitude of the imageblocker signal over a desired channel bandwidth as linear, determining atiming offset and a filter coefficient or multiplier.

In an exemplary scenario, the calibration process may be based onsymmetric adaptive decorrelation (SAD) algorithms to estimate thecoefficient over a certain bandwidth, although any signal decorrelationalgorithm may be used. The SAD method estimates the complex couplingcoefficients between the desired and blocker signals and the couplingcoefficients may then be deduced in an iterative process.

The compensation method may comprise a narrowband correction logic or awideband logic using multi-tap filters in time domain or equivalentlyusing frequency domain techniques using Fourier transform to applyfrequency-dependent correction once the timing mismatch is known.

FIG. 3 is a diagram illustrating alias signals from blockers resultingfrom timing offsets in a time interleaved analog to digital converter,in accordance with an embodiment of the invention. Referring to FIG. 3,there is shown a clock (0) signal and a clock (180) signal, which in anideal case are exactly 180 degrees out of phase. However, in realcircuits, non-uniformities in devices across a chip may result in timingoffsets between clock signals, which in a time interleaved ADC mayresult in aliasing of blocker signals onto the desired signals, asillustrated in the lower plots. The lower left plot shows the idealizedcase with no aliasing of the blocker signal onto the desired signal,whereas the lower right plot shows aliasing of the blocker signal ontothe desired signal when the clock signals are not exactly 180 degreesout of phase.

In an example scenario, the desired signal may be extracted from thereceived signal, which comprises both the desired signal and the blockersignal, through decorrelation techniques, such as symmetric adaptivedecorrelation or blind source separation, for example. The complexcoupling coefficients between signals may be determined utilizing thesetechniques, and the desired signal extracted utilizing the determinedcoefficients. In this manner, timing offsets may be mitigated in thedigital domain without the need for complex timing circuitry forminimizing offsets.

Aliasing of signals due to timing mismatch/offset may be modeled usingthe following relations:

${X(\omega)} = {\underset{\underset{{Desired} + {{Blocker}^{\prime}s\mspace{14mu} {image}}}{}}{{{K_{1}(\omega)}{S(\omega)}} + {{K_{2}\left( {\frac{\omega_{s}}{2} - \omega} \right)}{I^{*}\left( {- \omega} \right)}}} + \underset{\underset{{Blocker}\; + {{Desired}^{\; \prime}s\mspace{14mu} {image}}}{}}{{K_{1}\left( {\frac{\omega_{s}}{2} - \omega} \right){I\left( {\frac{\omega_{s}}{2} - \omega} \right)}} + {{K_{2}(\omega)}{S^{*}\left( {\omega - \frac{\omega_{s}}{2}} \right)}}}}$

where S(ω) is the desired channel, I(ω) is the blocker, and w representsfrequency. The coupling coefficients may be a function of frequency aregiven by:

${X(\omega)} = {\underset{\underset{{Desired} + {{Blocker}^{\prime}s\mspace{14mu} {image}}}{}}{{{K_{1}(\omega)}{S(\omega)}} + {{K_{2}\left( {\frac{\omega_{s}}{2} - \omega} \right)}{I^{*}\left( {- \omega} \right)}}} + \underset{\underset{{Blocker}\; + {{Desired}^{\; \prime}s\mspace{14mu} {image}}}{}}{{K_{1}\left( {\frac{\omega_{s}}{2} - \omega} \right){I\left( {\frac{\omega_{s}}{2} - \omega} \right)}} + {{K_{2}(\omega)}{S^{*}\left( {\omega - \frac{\omega_{s}}{2}} \right)}}}}$

Once the coupling coefficients are known, they may be compensated for insubsequent processing, thereby extracting the desired signal whileignoring the blocker signal, as described further with respect to FIG.4.

FIG. 4 is a diagram illustrating exemplary ADC timing offset estimationand compensation circuitry, in accordance with an embodiment of theinvention. Referring to FIG. 4, there is shown an alias correctionsystem 400 comprising a mixing system 410 and a symmetric adaptivedecorrelation (SAD) system 420. There is also shown input signals s(n)and i(n), which are the desired signal and the blocker image signal,respectively; intermediate signals d(n) and v(n), which are thedown-converted desired and blocker signals, respectively; and ŝ(n) andî(n), which are the desired decorrelated signal output and thedecorrelated blocker signal output, respectively. The signal and image,s(n) and i(n) may be communicated to the alias correction system 400from a crossbar, for example. The components in FIG. 4 may operateexclusively in the digital domain, or partially in the analog domain andpartially in the digital domain.

The mixing system 410 is a representation of aliasing mechanisms in adown-conversion process, and comprises a pair of coupling multipliers401A and 401B that are cross-coupled to the summers 403A and 403B toindicate the aliasing of signals in the mixing process. Accordingly, theoutput signals of the mixing system 410 comprise the sum of the expectedsignals, i.e., s(n) and i(n) summed with an image of the other signal,as illustrated by the output signals d(n) and v(n).

The symmetric adaptive decorrelation system 420 may comprise adaptivemultipliers, or filters, 405A and 405B that are cross-coupled to thesummers 407A and 407B, and a decorrelation module 409. The summers 407Aand 407B may comprise circuitry that is operable to add a plurality ofinput signals and output a combined output signal. In this manner, anappropriate input signal may be injected to cancel out unwanted signals.

The decorrelation module 409 may comprise circuitry, logic, and/or codethat is operable to determine coupling coefficients between receivedsignals, which may comprise one or more undesired blocker signalsaliased onto desired signals due to timing mismatch in a timeinterleaved ADC, for example. Accordingly, once the complex couplingcoefficients are determined, the decorrelation module 409 may beoperable to configure the multipliers 405A and 405B, which may generateoutput signals that may cancel blocker signals when added to the otherinput signal at the summer 407A or 407B. While two separate multipliers405A and 405B are shown, a simpler approach may utilize a singlemultiplier, such as a single tap filter with the single outputcommunicated to both summers 407A and 407B, which is as described in themathematical formulations below.

In an example scenario, the output signals d(n) and v(n) from the mixingsystem 410 may be communicated to the symmetric adaptive decorrelationsystem 420. The summers 407A and 407B may sum the received signals witha multiplier signal, W₁(z) and W₂(z), which may be configured by thedecorrelation module 409.

The SAD algorithm assumes that desired and undesired signals areuncorrelated, which is represented by the following relation:

E[s(k)i(k−m)]=0

where E is an expectation operator and s(k) is the desired signal andi(k) is the image of the undesired signal.

The mixing of these signals may cause aliasing of signals into the samefrequency range, resulting in blocker signals. The decorrelationalgorithm therefore decorrelates the desired signal from the aliasedimage of the undesired channel such that the estimates are uncorrelated:

E[ŝ(k)î(k−m)]=0

E[î(k)ŝ(k−m)]=0

A simplified model for the aliased signals assumes a linear multiplier:

d(n) = K₁₁s(n) + K₂₂i^(*)(n) v(n) = K₁₂i(n) + K₂₁s^(*)(n)where$K_{12} = {\frac{1}{2}\left( {1 + e^{{- {j{({\frac{\omega \; s}{2} - {\omega \; 0}})}}}\Delta \; t}} \right)}$$K_{22} = {\frac{1}{2}\left( {1 + e^{{- {j{({\frac{\omega \; s}{2} - {\omega \; 0}})}}}\Delta \; t}} \right)}$and  ω0 = 2π f 0

The cancellation of aliasing may be accomplished using two separate1-tap filters:

ŝ(n)=d(n)−w ₁ ·v*(n)

î(n)=v(n)−w ₂ ·d*(n)

which leads to:

ŝ(n)=(K ₁₁ −w ₁ K ₂₁*)s(n)+(K ₂₂ −w ₁ K ₁₂*)i*(n)

î(n)=(K ₁₂ −w ₂ K ₂₂*)i(n)+(K ₂₁ −w ₂ K ₁₁*)s*(n)

And solving for the optimal filter values:

${w_{1} = {\frac{K_{22}}{K_{12}^{*}} \approx K_{22}}},{w_{2} = {\frac{K_{21}}{K_{11}^{*}} \approx K_{21}}}$since  K₁₂ ≈ 1 ≈ K₁₁

In an example scenario, the timing mismatch may be estimated in a narrowband stage, which may be achieved utilizing a least mean squares updateof cancellation filter coefficients, w₁ and w₂, utilizing the relation:

w(k+1)=w(k)+2μ(m)ŝ(k)î(k)

where m is the step size, or bandwidth, of the update loop. Then thecorrection values may be programmed in a wideband stage in the receiversystem.

Furthermore, as a special case, a single converged filter coefficient wcan be used to estimate the timing mismatch given by a root of aquadratic equation, which may be closely approximated by:

$\left. {w \approx \frac{K_{21} + {GK}_{22}}{1 + G}} \right\} \begin{matrix}{{G1},} & {w \approx K_{22}} \\{{G1},} & {w \approx K_{21}}\end{matrix}$ ${{where}\mspace{14mu} G} = 10^{- \frac{DU}{10}}$

G represents the DU ratio (in dB) between the actual desired andundesired signals before aliasing, which may be measured with a receivedsignal strength indicator (RSSI) detector, for example. The timingmismatch may then be computed using the converged filter value and theestimate of actual DU between the signal and the blocker, as shownbelow:

${\Delta \; t} \approx \frac{2\left( {1 + G} \right) \times {{Im}(w)}}{2{\pi \left( {{G\frac{f_{s}}{2}} - {\left( {G - 1} \right)f_{0}}} \right)}}$

where f_(s) is the sampling frequency in Hz, f₀ is the desired channelcenter frequency in Hz, and Im(w) represents imaginary part of w.

The timing mismatch may be estimated differently for different ranges ofDU. For moderate absolute values of DU, such as less than or equal to 10dB, the timing mismatch may be approximated by:

${\Delta \; t} \approx \frac{\left( {1 + G} \right) \times {{Im}(w)}}{\pi \times \left( {{G\frac{f_{s}}{2}} - {\left( {G - 1} \right)f_{0}}} \right)}$

For cases with a strong blocker, for example if DU is less than −10 dB,the timing mismatch may be approximated by:

${\Delta \; t} \approx \frac{{Im}(w)}{\pi \left( {\frac{f_{s}}{2} - f_{0}} \right)}$

And for cases with a strong desired signal, such as when DU is greaterthan 10 dB, the timing mismatch may be approximated by:

${\Delta \; t} \approx \frac{{Im}(\omega)}{\pi \times f_{0}}$

Once Δt is known, the decorrelation module 409 may program themultiplier 405A and 405B with the correction values, or multipliers,W₂(z) and W_(i)(z), or a single value, w, for a single output multiplierfor the desired channel as:

$w_{opt} \approx {{- j}\; {\pi \left( {\frac{fs}{2} - f_{0}} \right)}\Delta \; t}$

This optimal correction value w_(opt) may then be applied to thereceived signals and communicated to the summers 407A and 407B to cancelout the undesired signals, resulting in the representations ŝ(n) andî(n) of the original signals s(n) and i(n).

FIG. 5 is a diagram illustrating exemplary ADC timing offsetcompensation-only circuitry in time-domain, in accordance with anembodiment of the invention. Referring to FIG. 5, there is shown amultiplier 505 and a summer 507. There is also shown input signals d(n)and v(n) and output signal ŝ(n). FIG. 5 illustrates the compensationblocks of the symmetric adaptive decorrelation system 420 described withrespect to FIG. 4, and shows the compensation process in the timedomain, in contrast to that of FIG. 6, which is in the frequency domain.

FIG. 6 is a diagram illustrating exemplary ADC timing offsetcompensation-only circuitry in frequency-domain, in accordance with anembodiment of the invention. Referring to FIG. 6, there is shown amultiplier 605 and a summer 607, similar to the multiplier 505 andsummer 507 of FIG. 5, except that they operate in the frequency domain,showing the flexibility in the compensation process. There is also showninput signals D(f) and V(f) and output signal ŝ(f). FIG. 6 illustratesthe compensation blocks of the symmetric adaptive decorrelation system420 described with respect to FIG. 4 but operating in the frequencydomain.

FIG. 7 is a flow diagram illustrating exemplary steps in an aliasingcompensation process, in accordance with an exemplary embodiment of theinvention. Referring to FIG. 7, there is shown a process flow startingwith start step 701 followed by step 703 where a calibration tone isgenerated for a foreground estimation and compensation or a regularsignal is received for a background estimation and compensation. In step705, the timing mismatch estimation may be initiated followed by step707 where the correction coefficient, such as the multiplier w describedabove, may be read from the alias cancellation algorithm.

The ratio of the signal strengths of the desired to undesired signalsmay be measured to compute DU in step 709, which may be utilized todetermine the appropriate relation to determine the timing mismatch instep 711, followed by end step 713.

In an embodiment of the invention, a method and system may comprisereceiving an analog signal on a chip 210, converting the analog signalto a digital signal utilizing a time interleavedanalog-to-digital-converter (ADC) 200, and reducing a blocker signalthat is generated by timing offsets in the time interleaved ADC 200 byestimating complex coupling coefficients between a desired digitaloutput signal and the blocker signal utilizing a decorrelation algorithmon frequencies within a desired frequency bandwidth. The decorrelationalgorithm may comprise a symmetric adaptive decorrelation algorithm. Anamplitude of the blocker signal may be approximated as linear within thedesired frequency bandwidth.

The received analog signal may be generated by a calibration tonegenerator 201 on the chip 220 for a foreground estimation andcompensation. A signal may be received from external to the chip for abackground estimation and compensation. Aliased signals may be summedwith an output signal from a multiplier 405A/405B. The complex couplingcoefficients may be determined utilizing the decorrelation algorithm onthe summed signals. The multiplier 405A/405B may be configured utilizingthe determined complex coupling coefficients. The blocker signal in thetime interleaved ADC 200 may be canceled utilizing the configuredmultiplier 405A/405B. The time interleaved ADC 200 may comprise two ADCpaths, ADC path 1 and ADC path 2, with clock signals, clock (0) andclock (180) that have 180 degree phase difference. The timing offsetsmay comprise a deviation in the 180 phase difference.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for timeinterleaved analog-to-digital converter timing mismatch estimation andcompensation.

Accordingly, aspects of the invention may be realized in hardware,software, firmware or a combination thereof. The invention may berealized in a centralized fashion in at least one computer system or ina distributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware, software and firmware may bea general-purpose computer system with a computer program that, whenbeing loaded and executed, controls the computer system such that itcarries out the methods described herein.

One embodiment of the present invention may be implemented as a boardlevel product, as a single chip, application specific integrated circuit(ASIC), or with varying levels integrated on a single chip with otherportions of the system as separate components. The degree of integrationof the system will primarily be determined by speed and costconsiderations. Because of the sophisticated nature of modernprocessors, it is possible to utilize a commercially availableprocessor, which may be implemented external to an ASIC implementationof the present system. Alternatively, if the processor is available asan ASIC core or logic block, then the commercially available processormay be implemented as part of an ASIC device with various functionsimplemented as firmware.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext may mean, for example, any expression, in any language, code ornotation, of a set of instructions intended to cause a system having aninformation processing capability to perform a particular functioneither directly or after either or both of the following: a) conversionto another language, code or notation; b) reproduction in a differentmaterial form. However, other meanings of computer program within theunderstanding of those skilled in the art are also contemplated by thepresent invention.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method for wireless communication, the method comprising: receiving an analog signal on a chip; converting the analog signal to a digital signal utilizing a time interleaved analog-to-digital-converter (ADC); and reducing a blocker signal that is aliased onto a desired digital signal by a timing offset in said time interleaved ADC, by estimating complex coupling coefficients between said desired digital signal and said blocker signal utilizing a decorrelation algorithm in timing offset estimation and compensation circuitry.
 2. The method according to claim 1, wherein the decorrelation algorithm comprises a symmetric adaptive decorrelation algorithm.
 3. The method according to claim 1, comprising approximating an amplitude of said blocker signal as linear within said desired frequency bandwidth.
 4. The method according to claim 1, comprising performing a foreground estimation and timing offset compensation by generating the received analog signal utilizing a calibration tone generator on said chip.
 5. The method according to claim 1, comprising performing a background estimation and timing offset compensation utilizing an analog signal received from external to said chip.
 6. The method according to claim 5, comprising estimating a change in said timing offset utilizing the background estimation and compensation.
 7. The method according to claim 1, comprising summing the aliased signal with an output signal from a multiplier.
 8. The method according to claim 7, comprising determining said complex coupling coefficients utilizing said decorrelation algorithm on said summed signals.
 9. The method according to claim 8, comprising determining said timing offset utilizing said determined complex coupling coefficients.
 10. The method according to claim 9, comprising configuring said multiplier with a value determined from said determined timing offset.
 11. The method according to claim 1, comprising cancelling said blocker signal utilizing the configured multiplier.
 12. The method according to claim 1, wherein said time interleaved ADC comprises two ADC paths with clock signals 180 degree phase difference.
 13. The method according to claim 1, comprising estimating said timing offset based on a ratio of amplitudes of a desired analog signal associated with said desired digital signal and an analog signal associated with the blocker signal.
 14. The method according to claim 1, comprising estimating a timing mismatch for a plurality of frequency channels utilizing said timing offset estimation and compensation circuitry.
 15. A system for wireless communication, the system comprising: one or more circuits on a chip comprising a time interleaved analog-to-digital-converter (ADC), wherein said one or more circuits are operable to: receiving an analog signal on said chip; converting the analog signal to a digital signal utilizing said time interleaved ADC; and reducing a blocker signal that is aliased onto a desired signal by timing offsets in said time interleaved ADC, by estimating complex coupling coefficients between said desired digital output signal and said blocker signal utilizing a decorrelation algorithm on frequencies within a desired frequency bandwidth.
 16. The system according to claim 15, wherein the decorrelation algorithm comprises a symmetric adaptive decorrelation algorithm.
 17. The system according to claim 15, wherein said one or more circuits are operable to approximate an amplitude of said blocker signal as linear within said desired frequency bandwidth
 18. The system according to claim 15, wherein said one or more circuits are operable to perform a foreground estimation and timing offset compensation by generating the received analog signal utilizing a calibration tone generator on said chip.
 19. The system according to claim 15, wherein said one or more circuits are operable to perform a background estimation and timing offset compensation utilizing an analog signal received from external to said chip.
 20. The system according to claim 19, wherein said one or more circuits are operable to estimate a change in said timing offset utilizing the background estimation and compensation. 